Protein: YL13B_YEAST

Transposon Ty1-LR3 Gag-Pol polyprotein

FUNCTION: Capsid protein (CA) is the structural component of the virus-like particle (VLP), forming the shell that encapsulates the retrotransposons dimeric RNA genome. The particles are assembled from trimer-clustered units and there are holes in the capsid shells that allow for the diffusion of macromolecules. CA has also nucleocapsid-like chaperone activity, promoting primer tRNA(i)-Met annealing to the multipartite primer-binding site (PBS), dimerization of Ty1 RNA and initiation of reverse transcription (By similarity). more...

FUNCTION: The aspartyl protease (PR) mediates the proteolytic cleavages of the Gag and Gag-Pol polyproteins after assembly of the VLP (By similarity).

FUNCTION: Reverse transcriptase/ribonuclease H (RT) is a multifunctional enzyme that catalyzes the conversion of the retro- elements RNA genome into dsDNA within the VLP. The enzyme displays a DNA polymerase activity that can copy either DNA or RNA templates, and a ribonuclease H (RNase H) activity that cleaves the RNA strand of RNA-DNA heteroduplexes during plus-strand synthesis and hydrolyzes RNA primers. The conversion leads to a linear dsDNA copy of the retrotransposon that includes long terminal repeats (LTRs) at both ends (By similarity).

FUNCTION: Integrase (IN) targets the VLP to the nucleus, where a subparticle preintegration complex (PIC) containing at least integrase and the newly synthesized dsDNA copy of the retrotransposon must transit the nuclear membrane. Once in the nucleus, integrase performs the integration of the dsDNA into the host genome (By similarity). CATALYTIC ACTIVITY: Deoxynucleoside triphosphate + DNA(n) = diphosphate + DNA(n+1). CATALYTIC ACTIVITY: Endonucleolytic cleavage to 5'- phosphomonoester.

SUBUNIT: The capsid protein forms a homotrimer, from which the VLPs are assembled. The protease is a homodimer, whose active site consists of two apposed aspartic acid residues (By similarity).

DOMAIN: The C-terminal RNA-binding region of CA is sufficient for all its nucleocapsid-like chaperone activities (By similarity).

DOMAIN: Integrase core domain contains the D-x(n)-D-x(35)-E motif, named for the phylogenetically conserved glutamic acid and aspartic acid residues and the invariant 35 amino acid spacing between the second and third acidic residues. Each acidic residue of the D,D(35)E motif is independently essential for the 3'- processing and strand transfer activities of purified integrase protein (By similarity).

PTM: Initially, virus-like particles (VLPs) are composed of the structural unprocessed proteins Gag and Gag-Pol, and contain also the host initiator methionine tRNA (tRNA(i)-Met) which serves as a primer for minus-strand DNA synthesis, and a dimer of genomic Ty RNA. Processing of the polyproteins occurs within the particle and proceeds by an ordered pathway, called maturation. First, the protease (PR) is released by autocatalytic cleavage of the Gag-Pol polyprotein yielding capsid protein p45 and a Pol-p154 precursor protein. This cleavage is a prerequisite for subsequent processing of Pol-p154 at the remaining sites to release the mature structural and catalytic proteins. Maturation takes place prior to the RT reaction and is required to produce transposition-competent VLPs (By similarity). MISCELLANEOUS: Retrotransposons are mobile genetic entities that are able to replicate via an RNA intermediate and a reverse transcription step. In contrast to retroviruses, retrotransposons are non-infectious, lack an envelope and remain intracellular. Ty1 retrotransposons belong to the copia elements (pseudoviridae).